This invention relates to a therapeutic bed of a radiotherapeutic system intended particularly for subjecting a patient to radiotherapy in a relatively shallow and wide area of an affected portion of the patient.
A general radiotherapeutic system comprises a radioactive ray irradiator and a radiotherapeutic bed. The radioactive ray irradiator has an irradiation head for irradiating radioactive rays of a desired nature. An irradiation axis of the radioactive rays irradiated from the irradiation head intersects with a central axis of the rotation of the irradiator, and this intersecting point is an isocentric point. On the radiotherapeutic bed is mounted a top board on which a patient is placed or laid to be movable up and down, left and right, back and forth.
There has been proposed one method of treating the affected portion of the patient by utilizing the radiotherapeutic system of the type described above, in which the radioactive ray irradiator is rotated with the affected portion being adjusted exactly to the isocentric point. As other treatment methods, recently, there has also been proposed a method in which the irradiation head is positioned below a top board of a radiotherapeutic table and irradiates therefrom with the irradiation head being directed upwardly.
In the latter method, the top board is lifted upward by about several tens cm in comparison with the former method and, in this state, the irradiator is rotated about its rotation axis with the irradiation head directed upward to thereby locate the irradiator below the top board. The irradiation is then carried out from the back side of the top board so as to cover a relatively wide range of the patient body with the location of the irradiator being maintained as it is.
The reason why such upward irradiation is required is as follows. That is, radioactive rays from the irradiation head are radiated in the form of quadrangular pyramid with the radiation source as a vertex, and therefore the radioactive rays will be applied more widely as the irradiation source moves away from the patient. Consequently, when such a system is not ready for upward irradiation, the irradiation head is positioned on an upper side of the top board when treating a patient for cutaneous cancer, for example, which is distributed extensively and almost the whole body of the patient is thus irradiated relatively in a wide range. The top board should be lowered extremely. In addition, when irradiating an affected portion distributed on the back side of the patient, it is obliged for the patient to be laid on his face, thus being inconvenient and troublesome.
Now, therefore, if an upward irradiation is to be realized, the top board need not be lowered extremely and the patient then need not be laid on his face. Accordingly, the treatment for the affected portion will be effected only through a vertical movement of the top board.
To realize such upward irradiation, it will be required that a top board of the therapeutic bed is positioned apart, by about 170 cm, for example, for achieving good working condition, from a floor level in a therapeutic room in which the therapeutic bed is located, particularly in consideration of a space of a general hospital construction.
To satisfy this requirement by using a therapeutic bed of so-called pedestal type not provided with a driving mechanism including struts and others elements under the floor, it is optimal to use a hydraulic link mechanism such as an oil pressure link mechanism with a liquid as a power means also in consideration of minimizing a height of the top board from the floor level for the motion of the patient. The therapeutic bed driving mechanism is generally accommodated in a space of a casing of the therapeutic bed disposed below the top board. That is, if the driving mechanism is constructed of a mechanical element such as a gear or the like, a bulk of each element increases unavoidably and, hence, the system itself becomes large as a whole in construction.
Meanwhile, in case a single-stage link mechanism is used as the oil pressure link mechanism for establishing a moving distance of the top board in vertical movement, it is required for the link mechanism to have prolonged arm members constituting the link mechanism accordingly. Thus, when it is required for the therapeutic bed to be displaced vertically, the lengths of the respective arm members of the link mechanism are accordingly prolonged, and when the therapeutic bed is vertically lowered, the arm members of the link mechanism lie substantially horizontally in the space of the casing supporting the top board, resulting in the requirement of the horizontally elongaged large space in the casing. Furthermore, a driving mechanism for driving the link mechanism is disposed in the space of the casing near the link mechanism of the conventional therapeutic bed. This location of the link driving mechanism in the space of the casing adversely results in the horizontal elongation of the therapeutic bed itself.
In order to ovbiate this defect of the single-stage link mechanism, in the conventional technology has been also provided a two-stage link mechanism including two pair of links, each being similar to that of the single-stage link mechanism, having arm members each having a length shorter than that of the single-stage link mechanism.
According to the application of the two-stage link mechanism, the link mechanism, as a top board elevating device, has been somewhat minimized, the link mechanism driving source is still positioned horizontally protrusively in the space of the casing. Thus, the link mechanism has still been left bulky as a whole. If a strut portion in which the link mechanism is present becomes large more than necessary, not only an operating efficiency of the apparatus deteriorates, but the space available for people is reduced.
As one example of a conventional therapeutic bed, the single-stage link mechanism has a horizontal length of about 1200 cm when expanded, the two-stage link mechanism is about 900 cm, and the driving mechanism is about 400 cm in the space of the casing of the therapeutic bed.